The first principle is the quadriga effect.
To understand the quadriga effect we have to first understand how we move our fingers.
There are two muscles that flex the 4 fingers, the flexor digitorum superficialis, or FDS,
and the flexor digitorum profundus, or FDP.
The FDP muscle inserts on the distal phalanx here, so when it contracts, it bends these
3 joints: the metacarpophalangeal joint or MCPJ, the proximal interphalangeal joint or
PIPJ, and the distal interphalangeal joint or DIPJ.
The FDS muscle inserts on the middle phalanx so it only bends the PIPJ and MCPJ.
Now that you know this, try this activity.
Grab your fingers and keep them straight with the other hand.
Now let go of both your ring and pinky fingers and try to bend them at all three joints.
For most people, what you'll notice is that the MCPJ and the PIPJ can flex without issue
but the DIPJs cannot.
Then try letting go of the middle finger.
Now you'll notice that you're able to magically bend all your DIPJs.
Why is this?
Well it's because the FDP tendons supplying the little, ring and middle fingers share
a common muscle belly in the forearm.
So it's an all or nothing type of situation - either all the fingers flex at the DIPJ
or none of them do, because it's the same muscle controlling all three of the fingers.
The index finger is special has it's own muscle belly within the FDP that allows it to flex
independent of the other three fingers.
In terms of rock climbing, this is important when climbers are holding onto one, two or
three finger pocket holds.
If the adjacent fingers are flexed in a pocket hold, it forces the FDP to contract more which
greatly increases the grip strength because they share that common muscle belly.
As opposed to keeping the fingers straight which means the FDP for the middle, ring and
pinky fingers cannot contract.
However, you have to be careful when harnessing the Quadriga effect because it causes a lot
of strain on the FDP and causes a shearing force on group of muscles called the lumbricals,
but that's a story for another video.
The next technique is the crimp grip which exploits the biomechanics of the pulley system
in the hand.
The flexor tendon are like this, they run along the fingers and when the muscle belly
contracts, it bends the fingers.
As you can imagine, there needs to be something holding the tendon close to the bone, like
how guides on a fishing rod keep the fishing line attached to the rod.
In the hand, there are ligaments called pulleys attached along the finger serving the same
purpose.
They keep the tendon close to the bone and allow for smooth gliding of the tendon.
Now rock climbers have multiple types of grips with the most common ones being the open grip
and the crimp grip.
The crimp grip is the most interesting because it's the strongest of all the different types
of rock climbing grips.
In this grip, the DIPJ is extended and the PIPJ is flexed.
To understand why this grip is so strong, we have to look at the positions of the tendons.
You'll notice it's forced to bend around two corners which causes more friction to be exerted
on the tendon.
Like if you twisted a rope between 2 poles, it causes more friction then wrapping it around.
So when the tendons are in the crimp position, the friction prevents smooth gliding of the
tendons and sort of locks them in place, resulting in increased grip strength.
This sounds great in theory but it puts a lot of strain on the pulleys and so if you
overuse the crimp grip, the pulley ligaments can strain or tear.
This most commonly happens here or here at the A2 or A4 pulley.
The A3 pulley at the joint is more flexible so can withstand the forces and is less commonly
injured.
However, if any of these pulleys completely tear the tendon will no longer be attached
to the bone leading to something called bowstringing because, well, it looks like a bowstring.
The final biomechanical technique, and arguably the most important one, is weight distribution.
If you draw a line from one arm to the opposite leg of a climber, that is their base of support.
The aim is to get the center of mass in line with the base of support.
This has two benefits.
One, it increases endurance because the weight can now be transferred to the stronger leg
muscles instead of the arms which tire out quickly.
And, two, it increases stability because it frees up your arms to reach for the next hold
without losing position.
One way climbers can align their center of mass with their base of support is simply
by twisting on one foot and moving their hips closer to the wall, in position called "hips
in".
Another way is by flagging, where one leg is stretched in the opposite direction to
where you want to go even if there's no foothold for that leg.
This might seem counterintuitive but it's effective in bringing the center of gravity
closer to the base of support as you can see here.
This reduces effort you have to put in and increases stability.
Now look what happens when you don't use a flag.
The arms have to compensate by working harder and a lot more energy is expended to complete
a basic move.
And after the move is completed, the body is unstable and in a biomechanically disadvantaged
position to complete the next move.
So that's the usual flag, but there's also something called a back flag where the non-weightbearing
leg goes behind the weightbearing leg.
This is used when the base of support is between the same side arm and leg.
If a flag is not performed, the body has a natural tendency to swing out which is called
a barndoor.
If a backflag is performed, the center of gravity moves in line with the base of support,
again increasing stability and freeing up an arm to reach for the next hold.
So in summary, there are three common biomechanical techniques used in rock climbing.
One is the quadriga effect which allows for stronger force generation through the FDP
tendons by flexing adjacent fingers.
The second one is the use of crimping to increases friction between the flexor tendon and pulley
ligaments, thereby improving grip strength.
And the third one is distribution of weight via flagging and hip movements to increase
stability and endurance.
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Thanks.